Electron discharge device



Dec. 5, 1933. E, E CHARLTQN 1,938,374

ELECTRON DISCHARGE DEVICE Filed Nov. 11 1922 JHEA'TERJ Inventor: ErnestE.Ch arlton,

2%2 His Attorney Patented Dec. 5, 1933 ELECTRON DISCHARGE DEVICE ErnestE. Charlton, Schenectady, N. Y., assignor to General Electric Company, acorporation of New York;

Application November 11, 1922 Serial No. 600,207

1 Claim.

The present invention comprises an improved electric discharge device ofthe non-self-sustainingtype, such as photo-electric devices.

Most photo-electric devices now in use contain a filling of fixed gas,such as argon or nitrogen. The current thus conducted varies withconditions such as applied voltage, intensity of illumination and soforth, but is never greater than a few hundred microamperes.

I have discovered that when an alkali vapor is used in discharge devicesin place of other gases, that currents of a higher order of magnitudemay be transmitted. Particularly favorable results can be obtained bytransmitting current through caesium vapor at an appreciable vaporpressure.

The accompanying drawing illustrates three embodiments of my invention.Figs. 1 and 2 show photo-electric devices containing a heater, thedevice of Fig. 1 having three electrodes, and therefore suitable as anamplifier and the device of Fig. 2 having two electrodes; Fig. 3 showsstill another modification with an external heating means.

The device shown in Fig. 1 comprises an envelope, or container 1,consisting of suitable refractory glass into which are sealed severalconductors. The conductor 2 leads to an electrode 3 capable of emittingelectrons when illuminated, preferably consisting of caesium, rubidium,although other alkali metal can be used. The conductors 4, 5, areconnected to a heater 6, consisting of a fine wire of tungsten, or othersuitable resistance material, and a conductor 7 leads to a controlelectrode 8, one end of which is sealed into the glass stem 9 which isconstituted by the flattened portion of the glass envelope. In thismodification the anode consists of a wire 10 which is sealed through thestem 9 and is surrounded by a sleeve 11 of glass within the envelopeexcept for an exposed tip which projects beyond the glass sleeve. It isalso possible to utilize the heater 6 as an anode when the heateroperates at so low a temperature that no electrons are emitted by it,thereby dispensing with a separate anode 10.

Fig. 2 shows a slightly modified device in which the cathode consists ofa cup 15 consisting of nickel-iron alloy, preferably copper coated,which is sealed into the container at 16, and is provided with a layer17 of caesium, rubidium, or other suitable alkali metal. The anode isconstituted by a wire 18 consisting of tungsten or other suitablematerial sealed into a stem 19 projecting through the side arm 20. Aheater 21 is connected to leading-in conductors 22, 23.

In the modification shown in Fig. 3, the cathode is constituted, by ametal disc 24 consisting of molybdenum, copper or nickel on which alayer of alkali metal is deposited. The anode 25 is constituted by awire sealedinto the side arm 26. An external heating means isdiagrammatically 69 indicated by the enclosure 27.

In the preparation of my improved photo-electrio device the glassenvelope or container is evacuated and baked out at about 450 C.according to the most improved methods of electron tube 55 exhaust. Whenthe interior has been thoroughly freed from water vapor and deprived ofgas an alkali metal, preferably caesium, is introduced from an externalchamber communicating with g the container 1. The drawing shows asealing off tube 12, which remains when the external chamber is removed,by heating the communicating tube to the softening point in the usualmanner. This external chamber (which is not shown) may contain a mixtureof caesium chloride and calcium by the interaction of which at anelevated temperature metallic caesium is formed which distills over intothe container 1 in a very pure state, both the main container and thereaction chamber being evacuated. When sufll- 99 cient caesium has beenintroduced the external chamber is removed without admitting foreigngas, and the tube 1 sealed off from the pump as indicated at the tube13.

Even at room temperature a greater photoelectric current is obtained indevices prepared in accordance with my invention containing caesium andrubidium when suitable potential is impressed between the electrodes 2and 10, and

the cathode is suitably illuminated. At elevated temperatures the devicewill conduct currents of higher order of magnitude than heretoforeconducted in photo-electric devices. For example, when the device isheated up to about 100 0. either by means of an internal heater, 9 asshown in the device in Figs. 1 and 2, or by externally applying heat, asindicated in Fig. 3, a photo-electric current of about five to fiftymilliamperes is obtained depending on conditions with an impressedelectromotive force of 300 about 250 volts, when illuminating thecathode by a lamp of about 750 candle power. While with operating bulbtemperatures from room temperature upward a substantial improvement incurrent with a given light source is obtained in the presence of purealkali metal vapor, preferably the operating temperature should besomewhere within the range of about 100 to 125 C.

The volt-ampere characteristics of my new device is positive, that is,as the voltage across the tube increases the current also increases.

The method of maintaining the temperature by means of a heater above thecaesium electrode, as shown in Figs. 1 and 2, is recommended instead ofan external heating space about the device, as thereby the neighborhoodof the cathode is maintained slightly cooler than the rest of the tube,and the alkali metal is caused to condense upon the cathode.

Cesium at a temperature of about 100 C. has a vapor pressure of aboutone micron. I find it is highly sensitive to the range of wave lengthsfound in ordinary light. When using rubidium as a photo-sensitivematerial a somewhat higher operating temperature is advisable, say, from120 to 150 C. For a given pressure, a temperature of about 10 C. higheris required for rubidium than for casium. V

A device such as shown in Fig. 1 containing current controllingelectrode 8 can be usedas an amplifier or radio detector by impressingupon the electrode 8 variable electric voltages or charges in the wellunderstood manner. I have obtained by this means good tones in atelephone circuitwhen using such a device in the reproduction of speechand music. For example, in Fig. l, I have shown an input circuit 28, 29containing the secondary of an input transformer 30 the primary of whichis supplied with the current to be amplified. The circuit 31, 32connected to the main electrodes 3 and 10 contains a source of current,represented by a. battery 33 and an electro-responsive devicerepresented by a telephone 34. During operation the cathode isilluminated by light of steady intensity either from an external sourceor derived from the internal resistor when operated at incandescence.

Where in the appended claims I have specifically included cesium vaporas the current carrying'medium, I wish also to include as equivalentsthe vapor of other alkali metals used in the absence of appreciableamounts of other or foreign gases in the discharge space of devicesoperating with a non-self-sustaining discharge. The metals caesium andrubidium are preferred because of their relatively high vapor pressureenabling them to be used more readily without attack of the containermaterial which conveniently consists of glass.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:-

A photo-electric tube comprising a container, electrodes thereinincluding a cathode, an anode and a control member, said cathodeconsisting of photo-sensitive material adapted'to be vaporized whenheated, means in said tube for heating said material, said meansincluding a heater element positioned nearer the control member than thecathode whereby the cathode is maintained at a lower temperature thanthe control member and the vaporized material is caused to condense at aposition remote from the control member.

I ERNEST E. CHARLTON.

